1. Field of the Invention
The present invention is directed to a relatively compact wide angle zoom lens system capable of providing a field angle approaching 84 degrees while sufficiently balancing the aberrations that occur over the entire range of zooming.
2. Brief Description of the Prior Art
The use of zoom lens systems have been becoming increasingly popular with amateur photographers and various examples are well known in the commercial market. As is well known by optical designers, the optimization of an image transmission through the zoom lens system for all points along the variable focal length is a constant problem. It is also well known that a zoom lens system is not readily adapted to a wide angle format particularly when it is also desired to maintain a relatively light weight compact lens system.
Finally, the competitive factor of cost competition adds a non-technological but nevertheless real limitation to the design variables that optical designers can utilize in maximizing their optical designs.
Various forms of two lens group zoom lens systems have been suggested in the prior art such as disclosed in the German Offenlegungsschrift of July 8, 1976; Japanese patent publication No. 40-8985; Japanese patent application laid open to public inspection No. 49-2548 and Japanese patent application laid open to public inspection No. 51-83543.
The German Offenlegungsschrift publication is of particular interest in that it discloses a two lens group zoom lens system wherein the first negative lens group is of a type which has a positive front component, a positive rear component and a negative component interposed between the front and rear lens components. The two lens group zoom lens system of this type is suitable for a zooming mode of operation in the range of wide angle photography since it provides a power distribution of a retrofocus type. However, the spherical aberration related to the higher order aberration coefficients tends to be insufficiently corrected when the lens system is set at the longest focal length. Additionally, substantial variation of aberrations such as distortion and coma occur during the variation of the focal length.
Thus, the prior art is still seeking to provide a relatively compact and economical wide angle two lens group zoom lens system with adequate optical correction.